JERUSALEM — Israeli warplanes struck inside Syrian territory Wednesday, U.S. officials reported, saying they believed the target was a convoy carrying sophisticated anti-aircraft weaponry on the outskirts of Damascus that was intended for the Hezbollah Shiite militia in Lebanon.

The U.S. officials, who spoke on the condition of anonymity, said Israel had notified the United States about the attack, which the Syrian government condemned as an act of “arrogance and aggression.”

Israel’s move demonstrated Israel’s determination to ensure that Hezbollah — its arch foe in the north — is unable to take advantage of the chaos in Syria to bolster its arsenal significantly.

The strike was the first time in more than five years that Israel’s air force had attacked a target in Syria. While no one expects the beleaguered Assad government to retaliate, the strike raised concerns that the Syrian civil war had spread beyond its border.

Regional security officials said the strike, which occurred overnight Tuesday, targeted a site near the Lebanese border, while a Syrian army statement said it destroyed a military research center northwest of the capital, Damascus. They appeared to be referring to the same incident.

Israeli officials would not confirm the airstrike, a common tactic. But it came after days of intense security consultations with Prime Minister Benjamin Netanyahu regarding the possible movement of chemical and other weapons around Syria, and warnings that Israel would act to thwart any possible transfers to Hezbollah.

Thousands of Israelis have crowded gas-mask distribution centers in the past two days. On Sunday, Israel deployed its Iron Dome missile-defense system in the north, near Haifa, which was heavily bombed during the 2006 war with Lebanon.

Syria and Israel are technically in a state of war but have long maintained an uneasy peace along their decades-old armistice line. Israel has mostly watched warily and tried to stay out of Syria’s civil war, fearful of provoking a wider confrontation with Iran and Hezbollah. In November, however, after several mortars fell on Israel’s side of the border, its tanks struck a Syrian artillery unit.

The U.S. State Department and Defense Department would not comment on reports of the strike.

The episode illustrated how the escalating violence in Syria, which has killed more than 60,000, is drawing in neighboring states and threatening to destabilize the region further.

Iran has allied itself with Assad, sending personnel from its Revolutionary Guards Quds Force to Syria and ferrying military equipment to Syria through Iraqi airspace. Hezbollah, which plays a decisive role in Lebanese politics and has supported Assad throughout the uprising, has long relied on Syria as a source of weapons and a conduit for weapons flowing from Iran.

Some analysts think Hezbollah may be trying to stock up on weapons now in case Assad falls and is replaced by a leadership that is hostile to the Shiite militia.

One U.S. official said the trucks targeted Wednesday were believed to have been carrying Russian-made SA-17 anti-aircraft weapons. Hezbollah’s possession of such weapons would worry Israelis, said Matthew Levitt, a former intelligence official now at the Washington Institute for Near East Policy.

“Israel is able to fly reconnaissance flights over Lebanon with impunity right now,” Levitt said. “This could cut into its ability to conduct aerial intelligence.”